Britain faces shortages of fuel, food and medicine, a three-month meltdown at its ports, a hard border with Ireland and rising costs in social care in the event of a no-deal Brexit, according to an unprecedented leak of government documents that lay bare the gaps in contingency planning.

The documents, which set out the most likely aftershocks of a no-deal Brexit rather than worst-case scenarios, have emerged as the UK looks increasingly likely to crash out of the EU without a deal.

Compiled this month by the Cabinet Office under the codename Operation Yellowhammer, the dossier offers a rare glimpse into the covert planning being carried out by the government to avert a catastrophic collapse in the nation’s infrastructure.

The file, marked “official-sensitive” — requiring security clearance on a “need to know” basis — is remarkable because it gives the most comprehensive assessment of the UK’s readiness for a no-deal Brexit.

It states that the public and businesses remain largely unprepared for no deal and that growing “EU exit fatigue” has hampered contingency planning which has stalled since the UK’s original departure date in March.

A senior Whitehall source said: “This is not Project Fear — this is the most realistic assessment of what the public face with no deal. These are likely, basic, reasonable scenarios — not the worst case.”

The revelations include:

● The government expects the return of a hard border in Ireland as current plans to avoid widespread checks will prove “unsustainable”; this may spark protests, road blockages and “direct action”

● Logjams caused by months of border delays could “affect fuel distribution”, potentially disrupting the fuel supply in London and the southeast of England

● Up to 85% of lorries using the main Channel crossings “may not be ready” for French customs and could face delays of up to two and a half days

● Significant disruption at ports will last up to three months before the flow of traffic “improves” to 50-70% of the current rate

● Petrol import tariffs, which the government has set at 0%, will “inadvertently” lead to the closure of two oil refineries, 2,000 job losses, widespread strike action and disruptions to fuel availability

● Passenger delays at EU airports, St Pancras, Eurotunnel and Dover

● Medical supplies will “be vulnerable to severe extended delays” as three-quarters of the UK’s medicines enter the country via the main Channel crossings

● The availability of fresh food will be reduced and prices will rise. This could hit “vulnerable groups”

● Potential clashes between UK and European Economic Area fishing vessels amid predictions that 282 ships will sail in British waters illegally on Brexit day

● Protests across the UK, which may “require significant amounts of police resource[s]”

● Gibraltar will face delays of more than four hours at the border with Spain “for at least a few months”, which are likely to “adversely impact” its economy

The revelations come as Boris Johnson signals that he would set a date for a general election after the UK has left the EU if Jeremy Corbyn succeeds in a vote of no confidence — preventing rebels from being able to stop a no-deal Brexit.

Johnson is preparing to hold talks with France’s president, Emmanuel Macron, and Angela Merkel, the German chancellor, ahead of this week’s G7 summit in Biarritz. But No 10 was last night playing down any prospect of a Brexit breakthrough and Germany believes no deal is “highly likely”.

The leak of the Yellowhammer dossier underlines the frustration within Whitehall over the lack of transparency surrounding preparations for leaving the EU. “Successive UK governments have a long history of failing to prepare their citizens to be resilient for their own emergencies,” said a Cabinet Office source.

The absence of a clear picture of the UK’s future relationship with the EU has hindered preparations as it “does not provide a concrete situation for third parties to prepare for”, the document states. Some of the bleakest predictions relate to goods crossing the French border. The file says that on the first day of no deal between “50% and 85% of HGVs travelling via the short channel straits [the main crossings between France and England] may not be ready for French customs, reducing the flow of freight lorries to between 40- 60%” of current levels”.

Unready lorries will “fill the ports and block flow” and the worst disruption to the main crossings could last for “up to three months before it improves by a significant level, to around 50-70%” of current levels.

Congestion may also occur at ports outside Kent and be exacerbated by the departure date, which coincides with the end of the October half-term holiday. Passengers at St Pancras, the Eurotunnel crossing and Dover may face delays as UK citizens travelling to the EU will face increased checks.

Despite Johnson repeatedly saying during the Tory leadership campaign that there will be “clean drinking water” in the event of no deal, the document raises the possibility that a failure in the chemical supply chain could “affect up to 100,000s of people”.